1. Field of the Invention
The present invention relates to an exterior environment recognition device and an exterior environment recognition method for recognizing environment outside of a subject vehicle.
2. Description of Related Art
Conventionally, a technique has been known that specifies a target object such as a vehicle, a person, and an obstacle located in front of a subject vehicle to avoid collision with the specified target object (brake control) and perform control so as to maintain a safe distance between the subject vehicle and the preceding vehicle (cruise control) (for example, Japanese Patent No. 3349060). In many of these techniques, a target object is tracked to update position information, and moving speed and the like of the preceding vehicle and the person is calculated. The result of this calculation is reflected in the brake control and the cruise control, for example.
Among these target objects, a person such as a pedestrian in particular is highly flexible in moving direction and moving speed as compared with a preceding vehicle, and moreover, the absolute volume of the person is small. For this reason, it is difficult to find the behavior of the person and track the person, and which makes it difficult to apply the technique to the brake control and the cruise control.
Accordingly, a technique has been known in which, in an image obtained by the subject vehicle, an area where movement is uniform is provisionally defined as an upper area, and a determination is made as to whether movements of feature points in a lower portion are not uniform. When the movements are determined to be non-uniform, the area is defined as a lower area, and a combination thereof is specified as a whole body area of a pedestrian (for example, Japanese Unexamined Patent Application (JP-A) No 2009-157581).
When the technique of Japanese Patent No. 3349060 is used, the whole body of a person can be specified in daylight. However, in a state where it is necessary to turn on headlights such as night, an effective image can be obtained only in a relatively low position of the whole body area of the pedestrian (the area of the lower half of the body) upon which lights of the headlights of the subject vehicle are incident, and it is impossible to specify an area where movements are uniform, which corresponds to the area of the upper half of the body. Therefore, for example, the whole body area of the pedestrian crossing in front of the subject vehicle cannot be specified, and this may cause problem in smooth operation of the brake control and the cruise control.